Suicide is the third leading cause of death among adolescents. Furthermore, the suicide rate for adolescents has more than doubled in the last 30 years. Prevention efforts targeted at the general population are likely to reach only a small number of teenagers who will eventually commit suicide. Consequently, a more sufficient strategy may be to target high-risk groups. The primary purpose of this study is to investigate suicidal thoughts and behaviors in offspring of depressed mothers (unipolar or bipolar depression) and offspring of parents with no history of a psychiatric disorder. A second objective is methodological, to determine what are the best methods for obtaining information on suicidality in children and adolescents. This study draws on a sample of 98 families that participated in an ongoing longitudinal study of the offspring of affectively ill and well mothers. Forty-two mothers were diagnosed with unipolar affective illness, 26 with bipolar affective illness and 30 were normal controls. Two children in each family were studied. Suicidality was assessed repeatedly in the younger cohort (at the ages of 6, 9, and 14 years) and the older cohort (6, 9, 13, and 18 years). Based on structured diagnostic interviews, suicidal ideation and behavior were categorized on a continuum as: Type I -- general suicidal ideation, Type II -- suicidal ideation with a plan or gesture, Type III -- suicidal attempts, Type IV -- completed suicides. The findings indicate that children of depressed parents are at risk for suicidality. The evidence is more consistent with regard to children of unipolar parents than bipolar parents. This may be in part attributable to the later onset of suicidality in children of the bipolar parents. Secondly, mothers with unipolar and bipolar depression differed in their ratings of child suicidality indicating that methodological issues are important in the assessment of suicidality in children and adolescents.